1. Field of Invention
The present invention relates to an electrostatic capacitance detection device that reads the surface contours of a fingerprint or other target object having extremely small ridges and valleys, by detecting electrostatic capacitance, which changes according to a distance from the surface of the target object.
2. Description of Related Art
As described in Japanese Laid Open to the Public No. Hei 11-118415, No. Hei 2000-346608, No. Hei 2001-56204, No. Hei 2001-133213, in electrostatic capacitance detection devices of the related art that are used in fingerprint sensors and so forth, a sensor electrode and a dielectric layer deposited on the sensor electrode are formed on a single-crystal silicon wafer. The principle of operation of an electrostatic capacitance detection device of the related art is shown in FIG. 1. One of a pair of electrodes in a capacitor is a sensor electrode the other is grounded to a human. Further, a dielectric layer is formed on the uppermost surface of the electrostatic capacitance detection device. The capacitance CF of this capacitor changes according to the ridges and valleys in a fingerprint contacting the surface of the dielectric layer. On the other hand, the semiconductor substrate is equipped with a capacitor that forms an electrostatic capacitance Cs. These two capacitors are connected in series, and a predetermined voltage is applied. The application of a voltage causes a charge Q corresponding to the ridges and valleys in a fingerprint to be formed between the two capacitors. This charge Q is sensed using ordinary semiconductor technology and the surface contours of the target object are read.